in the diagram below.A,B and C are three points in the same horizontal plane and AD is a vertical tower.AC=AB=x and DC=DB.the angle of elevetion of D from C is alpha and DB^C=theta

1.express DC in terms of x trigonometry value of alpha

2.prove that BC=2xcostheta/cos alpha

To solve this problem, we need to apply trigonometry and use the given information in the diagram. Let's go step by step:

1. Express DC in terms of x and find the trigonometry value of alpha:
In triangle ADC, we can see that angle ADC is right angled since AD is a vertical tower. Therefore, we can use trigonometry to relate the sides and angles of the triangle.

Using the trigonometric function tangent, we know that:
tan(alpha) = DC/AC

Given that AC is equal to x, we can rewrite the equation as follows:
tan(alpha) = DC/x

To find the value of DC, we can multiply both sides of the equation by x:
DC = x * tan(alpha)

Now we have expressed DC in terms of x, and we can move on to the next step.

2. Prove that BC = (2x * cos(theta)) / cos(alpha):
Let's analyze triangle DBC.

In triangle DBC, we can see that angle DBC is right angled since BC is a horizontal line. Therefore, we can use trigonometry to relate the sides and angles of the triangle.

Using the trigonometric function cosine, we know that:
cos(theta) = BC/DB

Given that DB and DC are equal, we can rewrite the equation as follows:
cos(theta) = BC/DC

We can rearrange the equation to solve for BC:
BC = cos(theta) * DC

Using the expression we derived in step 1 for DC, we can substitute it into the equation:
BC = cos(theta) * (x * tan(alpha))

Next, we can simplify the equation by multiplying the terms inside the parentheses:
BC = x * (tan(alpha) * cos(theta))

Now, recall the trigonometric identity tan(alpha) * cos(theta) = 2 * sin(alpha) * cos(alpha). We can substitute this into the equation:
BC = x * (2 * sin(alpha) * cos(alpha))

Finally, using the double angle formula for sine (2sin(alpha) * cos(alpha) = sin(2alpha)), we can rewrite the equation as:
BC = x * sin(2alpha)

Therefore, we have proven that BC = (2x * cos(theta)) / cos(alpha) using trigonometric identities and the given information.

By following these steps, you should be able to answer both parts of the question and understand the process behind it.